A. Field of the Invention
This invention relates to fuel caps for sealing the filler neck of fuel tanks of the type commonly found on automobiles, trucks and the like. More particularly, the invention relates to a fuel cap having a venting feature whereby the operator necessarily vents excessive pressure from the fuel tank before removing the cap from the filler neck, and also having a safety feature whereby once the cap is installed on the filler neck, rotational forces applied to the cap in either the cap installation direction or cap removal direction will not break the seal formed between the cap and the filler neck. The release of excessive pressure may be considered "selective" in the sense that the release occurs, as a preliminary step, when the operator elects to remove the cap.
B. Background Art
The fuel cap is a familiar item to anyone who operates gasoline powered motor vehicles. Nevertheless, the fuel cap is an important safety device for the vehicle. A cap must effectively seal the fuel tank so that harmful vapors do not escape into the environment. The cap must also be crashworthy and survive excessive rotational and translational forces as may be incurred in an accident. A cap should also not be subject to unintentional removal from the filler neck as may occur during a collision when rotational forces are applied to the cap in a cap-removal direction. Ideally, the cap should also provide for the selective release of excess pressure from the fuel tank prior to releasing the cap from the filler neck to prevent "geysering", the spillage of hot, flammable, fuel out of the filler neck due to pressure build-up in the tank when the cap is removed.
Considerable effort has been made in the art to produce a cap that achieves one or more of the previously stated objectives, but with varying degrees of success. The Evans patent, U.S. Pat. No. 4,177,931, discloses a "breakaway" fuel cap whereby the crown breaks away from the inner closure member upon the receipt of excessive forces in a collision. This patent, however, does not provide for selective release of pressure from the fuel tank, nor does it provide for selective driving engagement between the crown and the inner closure member in a cap-removal direction once the cap is installed on the filler neck. Another example of a breakaway type patent is U.S. Pat. No. 4,142,756 issued to Henning, et al. Other patents are directed to providing a breakaway feature to the cap whereby if the cap is subject to excessive translational forces, the crown breaks away from the housing, leaving the housing intact on the filler neck preventing the escape of fuel. These patents, however, generally do not provide for the selective release of pressure from the fuel tank or for selective driving engagement between the crown and the inner closure member.
The Harris patent, U.S. Pat. No. 4,830,058, discloses a fuel cap with a manually actuable clutch for selectively providing a driving connection between the outer shell and the closure portion or housing. The Harris patent, however, does not provide for a pressure relief valve for selectively relieving pressure from the fuel tank.
U.S. Pat. No. 4,736,863, also issued to Harris, discloses a ball-type pressure relief valve whereby the ball can be displaced from a sealed position to an open position by manually depressing a plunger. However, this cap does not provide the selective driving engagement features of the present invention whereby the threaded housing is selectively rotatably coupled to the crown.
Thus, it is clear that, heretofore, a fuel cap having all of the features of the present cap has eluded those in the art. The present invention supersedes the prior art fuel caps and provides in a novel fuel cap design the above-mentioned desired properties of a fuel cap, i.e., selective release of pressure from the fuel tank and selective driving engagement between the crown and the inner closure member or housing.